1. Field of the Invention
This invention relates to a portable power tool of the type which comprises an elongate tubular body supporting at a front end thereof a rotary cutter driven by an engine for mowing, and more particularly to such power tool which is improved to provide excellent operability.
2. Description of the Prior Art
As is well known, a typical portable power tool comprises an elongate tubular body connected at its rear end to an engine and supporting at its front end a rotary cutter at a fixed angle of e.g. 30 degrees relative to the tubular body The cutter is connected to the engine via a transmission shaft extending all the way through the tubular body.
In use of the power tool which is suspendingly shouldered by an operator, the tubular body is turned about its longitudinal axis by operating a handle provided on the tubular body, so that the cutter is altered in orientation to keep parallel to the slope and undulations of ground surface to thereby conduct uniform mowing. However, such operation for orientation change not only proves unsatisfactory for steep or severely undulating ground but also requires the operator to take an unnatural posture.
In view of the above drawback, Japanese Utility Model Publication No. 60-13322 (Published: Apr. 27, 1985; Application No.: 55-26838; Applicant: Yamada Machinery Industrial Co., Ltd.; Inventor: Sakuji Yamada) discloses a portable power tool which comprises a support tube fixed to an engine, and a slider tube axially slidably fitted in the support tube. The support tube is provided with a locking device consisting of a threaded shank with a gripping head, so that the slider tube is locked and unlocked relative to the support tube when the shank is tightened or loosened, respectively.
The slider tube is provided at an intermediate position thereof with a handle for facilitating axial movement of the slider tube. At a front portion of the slider tube is supported a connecting rod or prop bar which extends obliquely downward and forward and which is pivotally connected to a holder for a rotary cutter by means of a pin perpendicular to the longitudinal axis of the support tube and to the rotary axis of the cutter.
A flexible transmission shaft together with a flexible guide sheath extends through and out of the support tube and the slider tube to connect the engine to the cutter for rotation. Since the length of the guide sheath does not change, axial sliding movement of the slider tube relative to the support tube results in compression or tension of the guide sheath, causing the holder to pivot about the pin to vary orientation of the cutter.
The above described power tool, however, has a disadvantage that alteration in the orientation of the cutter requires at least three consecutive steps which include (1) loosening the threaded shank, (2) axially moving the slider tube relative to the support tube, and (3) tightening the threaded shank. Further, since the handle mounted on the slider tube has no expedient for reducing the force required to axially move the slider tube relative to the support tube, manipulation of the power tool is very laborious for the operator.